Singapore's Strait Times and AFP report that the messages caused share prices to fall by more than 2% and the South Korean won fell 0.88% cent against the US dollar.

The dramatic declines prompted the South Korean financial regulator and stock exchange to investigate suspicions of "unusual trade".

On Tuesday, South Korean police said: “We will continue to strictly probe stock price manipulation crimes aimed at disrupting equity-market order and doing harm to investors . . . The police and the Financial Supervisory Service will keep expanding the investigation.”

Earlier, AFP reported that three members of the group also pocketed 32 million won in early February, by spreading rumours that a new vaccine had been developed.